Coaxial high-frequency cable with internal spacers



Sept. 6, 1966 HORST-EDGAR MARTIN ETAL 3, 71,5 6

COAXIAL HIGH-FREQUENCY CABLE WITH INTERNAL SPACERS Filed March 23, 1965 United States Patent 6 Claims. (61. 174-28) Our invention relates to coaxial high-frequency cables Whose outer conductor is kept spaced and centered relative to the inner conductor by means of annular spacers seated on the inner conductor and axially spaced from each other.

There are known coaxial high-frequency cables, particularly transmitter-antenna cables for mediumand short-wave transmission of high power, in which the spacers are formed as full-bodied discs made, for example of polyvinylcarbazole. They are either injectionmolded upon the inner conductor or are separately produced and provided with radial slits to be positioned on the inner conductor. To reduce the amount of material in the spacers, it is known to form such spacers, molded onto the inner conductor, in the shape of a thin diaphragm reinforced by ribs.

It is an object of our invention to further improve coaxial high-frequency cables having mutually spaced spacers on the inner conductor. More specifically, it is an object of the invention to provide high-frequency coaxial cables with spacers of considerably smaller volume than those heretofore known, so as to decrease the dissipative attenuation of the cable and increase the transmittable amount of power.

According to our invention, the mutually spaced spacers in a coaxial high-frequency cable have a foot portion shaped as a C-shaped spring clip which is clampingly seated on the inner conductor about a major portion of its circumference and is engageable with the inner conductor by placing the clip transversely over the inner conductor. Furthermore, the spacer has radial legs extending away from the foot portion and forming support members at their respective extremities, the support members being peripherally spaced from each other for individually engaging the outer conductor. The entire spacer structure, comprising the foot portion and the legs with the support members, consists of an integral structure of insulating material.

By virtue of the fact that each spacer occupies a very small volume in comparison with the spacers heretofore employed, the attenuation of the coaxial high-frequency cable is considerably reduced and the corresponding reduction in losses has the result of-increasing the amount of transmittable power.

According to another, prefer-red feature of the invention, the legs whose outer extremities are provided with the abutment members, are given a cross-shaped cross section. As a result, the radial legs have an extremely high bending strength despite the minimized amount of material forming the legs.

It is further preferable, according to another feature of our invention, to provide means for preventing the C- shaped foot portion of the spacers from axial displacement on the inner conductor. A preferred way of doing this is to provide bosses or pointed protuberances on the inner surface of the C-shaped clip.

The invention will be further described within reference to a preferred embodiment illustrated by way of example in the accompanying drawing, in which:

FIG. 1 is a lateral view of an embodiment of a spacer of the present invention;

3,271,505 Patented Sept. 6, 1966 FIG. 2 is a view taken along the line IIII of FIG. 1; and

FIG. 3 shows schematically in perspective a high-frequency power cable according to the invention with spacers as shown in FIGS. 1 and 2.

The foot portion 1 of the illustrated spacers is designed as a C-shaped spring clip (also called Seegerring) and extends over a circular arc of about 270. The foot portion carries three legs 2, 3 and 4 angularly displaced from each other and extending radially away from the foot portion. The outer extremity of each leg is shaped as an abutment member 5. The foot portion 1 is seated on the inner conductor 10 of the high-frequency cable.

.The abutment members 5 engage the outer conductor 12 of the cable. The legs 2, 3 and 4 have an X-shaped cross section so as to possess high bending strength. Preferably and as shown, the axial length of the abutment members 5 is considerably larger than the corresponding length of the foot portion 1, and the corresponding Web sections of the legs taper from the larger length of the abutment members 5 down to the shorter length of the foot portion 1 in a symmetrical cross-sectional configuration.

Due to the C-clip design of the foot portion 1, the spacer can be readily forced or placed from the side onto the inner conductor 10 of the coaxial cable so that it surrounds the major portion of the periphery with a clamping fit. For fixing the position of the spacer in the axial direction, the inner surface of the C-clip is provided with inwardly protruding and pointed bosses 6 which enter into grooves or recesses of the inner conductor 10.

Since the spacers, once seated, are fixed relative to the inner conductor, the spacers as shown in FIGS. 1 and 2 are particularly well suitable for use with high-frequency cables whose outer conductor has a corrugated design or may possess a sectional shape in the form of a continuous wave. With a corresponding corrugated design of the inner conductor, the bosses located on the foot portion of the spacer and serving to prevent axial displacement of the spacer, may also be designed or arranged in form of a screw thread corresponding to the helical waviness of the inner conductor.

However, if the inner conductor of the high-frequency cable has a smooth surface, it is preferable to provide the inner conductor with embossed or pressed recesses to be engaged by the protuberances of the spacer foot, so that axial displacement of the spacer is reliably prevented. In cases where the clamping engagement of the spacer with the inner conductor is not sufficient, the ends of the C-clip structure may also be prevented from displacement by an additional clamp.

The spacer structure according to FIGS. 1 and 2 preferably consists of a single integral piece of synthetic plastic. The particular shape shown in FIGS. 1 and 2 permits producing the spacer by injection molding, thus affording an economical mass production of the spacers.

For transmitting high power at high frequencies, the material to be used for the spacers in high-frequency cables must be highly resistant to continuous heating, and the material must be mechanically strong to reliably se* cure an accurate support of the inner conductor in properly centered position. The material is further required to possess a small electrical loss angle and a low dielectric constant so that the dissipation losses due to attenuation remain slight. These requirements are satisfied, for ex ample, by making the spacer of the above-mentioned polyvinylcarbazole which is also well suitable for injection molding and accurately retains the desired measurements.

High-frequency cables according to the invention further possess the advantage that forces acting in the axial direction are better taken up by the twist-resistant legs than by the known full-disc or diaphragm-type spacers.

Furthermore, during production of such cables, the danger of breakage when forcing the spacers upon the inner conductor is considerably reduced.

We claim:

1. In a coaxial high-frequency cable having an inner conductor and an outer conductor coaxially surrounding the inner conductor, a plurality of annular spacers coaxially seated on said inner conductor and axially spaced from each other, each of said spacers comprising a foot portion forming a C-shaped spring clip clampingly seated on said inner conductor about a major portion of its circumference in engagement with said inner conductor, a plurality of angularly spaced legs extending radially away from said foot portion, each of said legs having a substantially cross-shaped cross-sectional area, and respective support members formed at the outer ends of said legs, said members being uniformly spaced from each other peripherally and individually engaging said outer conductor, said foot portion and said legs with said support members forming jointly an integral structure of insulating material.

2. In a coaxial-cable spacer according to claim 1, said support members having greater length in the axial direction than said foot portion, and said respective legs tapering from the length of said respective support members down to the shorter length of said foot portion.

3. A coaxial-cable spacer according to claim 1, comsaid foot portion on said inner conductor.

References Cited by the Examiner UNITED STATES PATENTS 2,274,031 2/1942 Bannon l74-28 X 2,424,388 7/ 1947 Duna.

FOREIGN PATENTS 647,150 7/ 1937 Germany. 656,267 2/ 1938 Germany.

OTHER REFERENCES The Condensed Chemical Dictionary, Sixth Edition, Reinhold Publishing Corp., New York, 1961, Q.D. 5 C5, p. 921.

LEWIS H. MYERS, Primary Examiner.

JOHN F. BURNS, Examiner.

D. A. KETTLESTRINGS,Assistant Examiner. 

1. IN A COAXIAL HIGH-FREQUENCY CABLE HAVING AN INNER CONDUCTOR AND AN OUTER CONDUCTOR COAXIALLY SURROUNDING THE INNER CONDUCTOR, A PLURALITY OF ANNULAR SPACERS COAXIALLY SEATED ON SAID INNER CONDUCTOR AND AXIALLY SPACED FROM EACH OTHER, EACH OF SAID SPACERS COMPRISING A FOOT PORTION FORMING A C-SHAPED SPRING CLIP CLAMPINGLY SEATED ON SAID INNER CONDUCTOR ABOUT A MAJOR PORTION OF ITS CIRCUMFERENCE IN ENGAGEMENT WITH SAID INNER CONDUCTOR, A PLURALITY OF ANGULARLY SPACED LEGS EXTENDING RADIALLY AWAY FROM SAID FOOT PORTION, EACH OF SAID LEGS HAVING A SUBSTANTIALLY CROSS-SHAPED CROSS-SECTIONAL AREA, AND RESPECTIVE SUPPORT MEMBERS FORMED AT THE OUTER ENDS OF SAID LEGS, SAID MEMBERS BEING UNIFORMLY SPACED FROM EACH OTHER PERIPHERALLY AND INDIVIDUALLY ENGAGING SAID OUTER CONDUCTOR, SAID FOOT PORTION AND SAID LEGS WITH SAID SUPPORT MEMBERS FORMING JOINTLY AN INTEGRAL STRUCTURE OF INSULATING MATERIAL. 